Automated Ultrashort Echo Time ( <scp>UTE</scp> ) <scp>MRI</scp> Low Signal Volume Analysis in Stable Pediatric Cystic Fibrosis and After Elexacaftor/Tezacaftor/Ivacaftor Therapy

ABSTRACT Background Ultrashort echo time (UTE) MRI overcomes the low signal intensity and short T 2 * of pulmonary tissues, improving image quality. Abnormally low UTE signal intensities are associated with hallmarks of cystic fibrosis (CF), including gas trapping and lung hyperexpansion. Purpose To explore short‐term repeatability and sensitivity to treatment of low signal volume (LSV) from UTE MRI in pediatric CF. Study‐Type Single‐site, retrospective, longitudinal. Subjects Thirteen participants with stable CF (6M/7F, median age = 15 years old) were scanned at baseline and 1‐month to evaluate short‐term repeatability. Subsequently, 14 CF participants (7M/7F median age = 16 years old) were scanned pre‐ and 1‐month post‐initiation of elexacaftor/tezacaftor/ivacaftor (ETI). Field Strength/Sequence Three‐dimensional stack‐of‐spirals for UTE, 2‐dimensional gradient‐echo for hyperpolarized xenon (Xe‐MRI), 3‐dimensional gradient‐echo for thoracic cavity estimation at 3 T. Assessment LSV was analyzed from UTE MRI. Same‐day spirometry, multiple‐breath washout, and Xe‐MRI were also performed to compare to LSV. Statistical Tests Differences were assessed with the Wilcoxon matched‐pairs signed‐rank test. Bland–Altman analysis and the Intraclass Correlation Coefficient (ICC) were used to assess 1‐month repeatability in stable CF. Relationships between measures were assessed with Spearman correlation. p < 0.05 was considered significant. Results Baseline LSV was correlated with forced expiratory volume in 1 s (FEV 1 ), FEV 1 to forced vital capacity ratio (FEV 1 /FVC), lung clearance index (LCI), and ventilation defect percent (VDP) (all | ρ | ≥ 0.50). LSV was not significantly different after 1‐month (20.1 [10.9–25.5]% vs. 21.7 [12.7–28.2]%, p = 0.4548) in stable pediatric CF with Bland–Altman bias < 1% and ICC = 0.93. LSV was significantly reduced from 18.8 [12.0–30.3]% to 16.4 [7.8–19.6]% after 1‐month of ETI and correlated with absolute differences in FEV 1 , FEV 1 /FVC, LCI, and VDP (all | ρ | ≥ 0.59). Data Conclusion LSV analysis was feasible and repeatable in pediatric CF over a 1‐month period. LSV was significantly reduced 1‐month after ETI treatment, indicating sensitivity to reduced gas trapping, hyperexpansion, and obstruction. Evidence Level 4. Technical Efficacy 1.